1. Technical Field of the Invention
The present invention is directed to methods and systems for locating and monitoring the status of people and moveable assets, such as first responders, including firefighters and other public service personnel, and their equipment both indoors and out. More specifically, the invention can provide for locating, and monitoring the status of, people and assets in environments where GPS systems do not operate, or where GPS operation is impaired or otherwise limited.
2. Description of the Prior Art
Global Positioning Systems (GPS) are well known systems for locating and monitoring people and assets. However, public GPS operation is limited in its accuracy by design for various reasons, including for national security. Further, the operation and accuracy of a GPS can be further limited by environmental conditions, for example, urban environments can block or limit GPS satellite signals. For the same reasons, GPS may not operate indoors.
Navigation systems and methods are typically used to provide position and tracking information for vehicles in land, sea and aerospace environments. Recently, there has been increased interest in providing navigation and tracking information on individuals moving in an indoor environment. Applications include, but are not limited to, identifying and locating individuals, pathways and exits in complex building structures during emergency situations and identifying and tracking emergency personnel in emergency search and rescue operations.
A variety of methods well-known in the art have been utilized for navigating and tracking moving vehicles in land, sea and aerospace environments. These include various forms of radio navigation methods, transponders, long range navigation beacons (LORAN), radio detection and ranging systems (RADAR), radio frequency identification and fixing, global positioning system tracking (GPS and DGPS) and space-based systems employed by the military. Typically such methods require that a moving vehicle to be equipped with radio transmitter or transceiver where location is determined by measurement of time delays of coded signals from multiple source transmitters at known stationary or moving positions. Such methods are typically limited to low power, line-of-sight transmission of weak signals between a transmitter and receiver and tracking may be compromised by local natural topological features or man-made structures, such as buildings, where weak signals are either obscured or severely attenuated.
While the Global Positioning System (GPS) has proved to be a useful navigation and tracking tool for outdoor tracking of moving vehicles, there are significant limitations when applying GPS to indoor navigation and tracking. Since GPS relies primarily on a line of sight signal acquisition and tracking, in indoor environments, the line of sight of GPS satellites is substantially obscured and GPS signals are highly attenuated. As a result, GPS signals are typically several orders of magnitude weaker in building environments than outdoors. With such weakened signals, GPS receivers have difficulty receiving GPS signals and calculating accurate position information.
In conventional vehicle navigation applications, both inertial and non-inertial sensor devices, such as compasses, barometers, gyroscopes and accelerometers, are frequently combined for navigation purposes. Compasses are frequently found on passenger vehicle dashboards. Barometer altitude measurements and compass direction measurements are required instruments on aircraft control panels. Inertial sensor device combinations are commonly employed in attitude and heading reference systems (AHRS), where vertical and directional gyroscopes are combined to provide measurements of role, pitch and heading (azimuth) angles, vertical gyroscopes (VG), rate gyro accelerometer units (RGA) and inertial measurement units (IMU). At least one company offers an AHRS system which combines 3-axis angular rate, linear acceleration, and magnetic field measurements to create an electronically stabilized AHRS device (see Crossbow Technology Inc, San Jose, Calif.). Vertical gyroscopes devices are commercially available which employ mechanically-gimbaled gyroscopes that are electronically stabilized to provide measurements of roll and pitch angles relative to the horizon. Single axis yaw rate gyros and 3-axis accelerometers are frequently employed in systems used for dead reckoning and controlling roll and pitch in land vehicles and robots.
Inertial measurement units (IMU), comprising of combination of accelerometers and gyroscopes, are frequently combined with control systems as critical components of an inertial navigation system (INS) for vehicles. The IMUs may be either mounted in a gimbaled servo motor system, where the control system keeps an IMU platform mounted in a constant orientation and vehicle orientation is determined from motion relative to the IMU, or, alternatively, IMUs may be mounted in a strap-down system where IMU sensor outputs provide a direct measurement of vehicle orientation. In typical applications, IMUs are generally employed with objects that move in relatively normal and smooth pattern, such as planes, land vehicles and machinery. For example, for aircraft navigation, inertial sensor combinations are frequently deployed in mechanically and thermally stabilized INS or IMU packages which typically combine three axes servo accelerometers and three axes rate gyros for vehicle motion sensing and navigation in free space where six degrees of freedom are required.
More recently, efforts have attempted to integrate inertial IMUs with GPS systems for vehicle, aviation, weapon and robotic navigation during periods when GPS signals are unreliable (see Y. C. Lee et al., “A Performance Analysis of a Tightly Coupled GPS/Inertial System for Two Integrity Monitoring Methods”, CAASD Technical Paper, March 2000, MITRE Corp. McLean, Va.; A. K Brown et al. “Performance test Results of an Integrated GPS/MEMS Inertial Navigation Package”, Proc. ION GNSS, September 2004, Long Beach; and P. Cross et al. “Intelligent Navigation, Inertial Integration: Double Assistance for GPS”, GPS World, May 1, 2002). In addition, efforts have been made to develop MEMS-based IMU navigation systems some of which use GPS for initial position calibration and periodic correction (see Honeywell H G 1900 MEMS IMU data sheet, Honeywell Corp.; Atair INU data sheet, Atair Aerospace, Brooklyn, N.Y.; MEMSense PINU and nINU data sheets, MEMSense LLC, Rapid City, S. Dak.; coremicro AHRS/INS/SPS data sheet, American GNC Corp., Simi Valley, Calif.).
Thus far, reliable methods for accurate personal indoor tracking and navigation have been very limited because, unlike vehicle motion, human movement is characteristically complex, non-linear and erratic. A review of indoor navigation methods and capabilities for emergency personnel has been conducted by researchers at the National Institute of Standards and Technology (see L. E. Miller, Indoor Navigation for First Responders: A Feasibility Study, Advanced Networking Technologies Division Report, Feb. 10, 2006 NIST, Washington, D.C.). In this study, well-known navigation techniques such as dead reckoning, waypoint detection and map matching are reviewed and discussed as to their viability in an indoor navigation environment.
While the NIST report identifies a number of INU devices and methods which have been recently developed for indoor tracking of individuals, the most common tracking methods employed by current workers utilizes dead reckoning navigation techniques which employ a fairly inaccurate method of integrating acceleration data over time. Due to accelerometer drift error, such tracking methods typically accumulate large amounts of error in a relatively short period of time, dead reckoning methods are inherently unreliable and location tracking must be frequently corrected using fixed waypoints that have a known, pre-determined position. In addition, for tracking highly non-linear and erratic human movements, such methods are inherently unsuitable since error accumulates too quickly which makes waypoint correction unfeasible. Furthermore, many of these devices suffer from inaccurate calibration and zero point determination.